**Core Concept**
Ghrelin and insulin are key hormones involved in regulating appetite and glucose metabolism in humans. Ghrelin stimulates appetite and increases food intake, while insulin suppresses appetite and promotes glucose uptake in the body.

**Why the Correct Answer is Right**
When the student became hungry, her ghrelin levels increased rapidly, stimulating her appetite and driving her to consume food. After she finished her snack, the insulin levels increased, suppressing her appetite and promoting glucose uptake in the body. Ghrelin levels decrease in response to food intake, while insulin levels increase. This is a normal physiological response to eating.

**Why Each Wrong Option is Incorrect**
**Option A:** Glucagon is a hormone that raises blood glucose levels by stimulating glycogen breakdown and gluconeogenesis. It does not play a direct role in regulating appetite or food intake.

**Option B:** Adrenaline (epinephrine) is a hormone involved in the "fight or flight" response, which can stimulate appetite in some individuals. However, it is not the hormone that increases rapidly in response to hunger and decreases promptly after eating.

**Option C:** Somatostatin is a hormone that inhibits the release of other hormones, including insulin and ghrelin. It does not play a direct role in regulating appetite or food intake.

**Clinical Pearl / High-Yield Fact**
Remember the "Ghrelin-Insulin Axis": Ghrelin increases appetite and food intake, while insulin suppresses appetite and promotes glucose uptake. This physiological response is essential for maintaining energy balance and glucose homeostasis in the body.

**Correct Answer:** . Ghrelin